Yes and no.
Film can stand very long exposure going into the hours, BUT it suffers from something called recperocity failure. The longer the exposure the lower its speed goes.
This effect can be avoided or slowed by super cooling the film holder.

For general astro photography the rebel will do OK, you need a mount capable of tracking and guideing to keep the target centered over long exposures. And it will suffer in the low red end of the spectrum, same as the 5d. The 20Da is specialized and a bit expensive.

I don't think that film can detect the infra-red spectrum. You will need to get really long telephoto lenses for your SLR camera, if you don't want to use the telescope. (Unless you don't mind shooting wider)

Question 1, Rebel 35, no not too good, these cameras chew the power while the shutter is open and do not last long on a bettery.
An old full manual camera that does not use batteries is much better.
Also technology has advanced in DSLR's and they perform better on their power sosurces now, that the old 35mm film cameras like the rebels ever did.

Question 2, Flash, flash has a effective distance of a few feet, space is big, really big. Flash won't reach anything and if it did somehow manage to, it could take years for the light to travel there and back. So leave the flash off.

Question 3, use the Rebel 35mm to shoot the moon, yes, use a 28-80mm yes but the moons image will be a tiny spec in the picture.

Film has no trouble with infrared if you use the right film type.
You can get film for both IR black and white and IR false color. Also the normal film responds much better to IR than unmodified DSLR's.

This photo wasn't captured by me, I have found it from another forum. (Sorry, Ican't exactlyremember who shot it)

BTW, it would be a better idea to utilize your telescope for such shots,rather than to buy long lenses for your SLR, or dSLR. (Because a telescope is anytime longer, thanlong telephoto lenses for cameras;whichusually cost a lot as well)

Therewas a solar filter over the lens, and you can also see the planet Mercury+ a large sunspot in the photo.

I need to caution that the sun is very bright (much brighter than you can imagine), and it can damage your equipments+ cause permanent blindness to your eyes (Juston sea levelalone, without zooming in); so you need to be very careful when dealing with solar photography.

[Do keep in mind that the Sun also emits various kindsradiation wavelengths from the electromagnetic spectrum; other than just emitting visible light raysalone]

Here is a site that shows the posibilities of the various cameras
The images so far on this November challenge all were done with Canons DSLR's
I see the 300D 350D 20D 20Da and 30D showing up in the image detailes.

I should add that at this level of astrophotography almost all of them indicate they have had the "Hutech Mod" (or similar) done (very expensive) that makes them mostly unsuitable for normal terrestrial photography.